1. Field of the Invention
The present invention relates generally to photoelectric sensors and, more specifically, to a circuit for a photoelectric sensor which provides a series of light pulses and changes the frequency of the light pulses in response to a change in the status of a light sensitive component of the photoelectric sensor.
2. Description of the Prior Art
Photoelectric sensors are well known to those skilled in the art. Many different types of photoelectric sensors and sensor applications have been used to monitor the movement of objects. As is known to those skilled in the art, photoelectric sensors can be provided with a means which pulses a light source to create a series of light pulses emanating at a preselected frequency from a light source, such as a light emitting diode. The pulsing of the light source is coordinated with a light sensitive component, such as a photodiode, so that the receipt of a light pulse by the light sensitive component can be coordinated with the timing of the energization of the light source. The purpose of this coordination is to provide the ability to distinguish the receipt of a legitimate light pulse from the receipt of background light emanating from some external source. If a light pulse is received by the light sensitive component coincidently with the transmission of a light pulse from the light source, related electronic circuitry is configured to accept the light pulse as indicating an unobstructed path between the light source and the light sensitive component. In certain applications, the light source is disposed within a first housing and the light sensitive component is disposed within a second housing. Alternatively, the light source and the light sensitive component can be disposed within a common housing and a reflective object can be used to receive light emanating from the light source and reflect light it back toward the light sensitive component within the same housing. The particular application of the photosensor which incorporates the present invention is not limiting the circuitry described below in relation to the preferred embodiment of the present invention.
U.S. Pat. No. 5,115,129, which issued to Johnson on May 19, 1992, describes a photoelectric sensor which comprises a light emitting diode and a light sensitive component disposed within a common housing. The housing is provided with a light transmissive end portion that is formed to provide one or more lenses. The lenses are formed as an integral part of the housing structure in order to facilitate manufacture and avoid the need for sealing components to prevent leakage into the housing when the photoelectric sensor is used in harsh duty applications that require washdown with high velocity fluids.